The present invention relates to gaskets to make a highly reliable pressure-tight joint between stationary parts at elevated temperatures and under high pressure.
In general, cylinder-head gaskets which are placed between cylinder blocks and cylinder heads have been fabricated by punching into a suitable configuration a gasket-sheet consisting of a wire gauze or metal sheet formed with hooks which is coated with asbestos or a rubber-asbestos mixture or a soft sheet consisting of a mixture of rubber and asbestos. The cylinder-head gaskets are generally subjected to high temperatures, and a considerably high temperature difference between an inlet port and an exhaust port causes thermal distortions of the mating surfaces of the cylinder block and the cylinder head and consequently the pressures acting on these mating or joint surfaces change from one point to another. However, since the cylinder-head gaskets are flat, they cannot absorb the thermal distortions of the mating or joint surfaces so that gas, water and oil leakages result.
Furthermore the unsuitable selection of the positions of studs joining the cylinder head and cylinder block, with respect to bores result in the uneven pressure distributions between the mating surfaces so that the pressure-tight joint effect is adversely affected. To solve this problem, the bolt-tightening force is increased to increase the pressures acting on the cylinder-head gasket, but this method frequently results in excessive pressures exceeding a limit of the gasket. As a consequence, the gasket is partially broken or collapsed, resulting in gas, oil or water leakage.
In addition, the conventional gaskets containing rubber have been presenting a pollution problem because not only the recovery of rubber from the gaskets is impossible but also there has been no suitable disposal method for wasted gaskets.
Therefore there has been a growing demand for gaskets which may ensure a highly reliable pressure-tight joint between the cylinder head and cylinder block even when the thermal distortions occur.